Types Of Polyamide Research Articles

The Activation Energy Of Ignition Calculation For Materials Based On Plastics

Abstract This article deals with the activation energy of ignition calculation of plastics. Two types of polyamide 6 and one type of polypropylene and polyurethane were selected as samples. The samples were tested under isothermal conditions at several temperatures while times to ignition were observed. From the obtained data, activation energy relating to the moment of ignition was calculated for each plastics. The values for individual plastics were different. The highest activation energies (129.5 kJ.mol−1 and 106.2 kJ.mol−1) were achieved by polyamides 6, while the lowest was determined for a sample of polyurethane.

Fast-scanning calorimetry of electrospun polyamide nanofibres: Melting behaviour and crystal structure

This paper discusses the melting behaviour and crystal structure of electrospun (polymorphous) polyamide (PA) fibres and presents the importance of the heating rate used for their study by thermal analysis. A case study of PA6, PA46 and PA69 nanofibres is performed using a Rapid Heat-Cool DSC (RHC), a fast-scanning calorimeter capable of controlled heating rates above 1000 K min−1. Thermal lag becomes significant at scan rates above 500 K min−1 and the ideal scan rate for analysis of the crystal structure depends on the PA type. Measurements at the most suitable heating rate indicate that the thermal stability of the crystals is higher for nanofibres compared to bulk material. Additionally, more stable crystals are favoured in finer nanofibres. This is especially the case for PA6 nanofibres, having an increasing fraction of stable α-crystal phase with decreasing fibre diameter, as shown by both thermal analysis and X-ray diffraction.

Effect of nanofibres on the curing characteristics of an epoxy matrix

Recently it is shown that nanofibrous structures have the potential to enhance the mechanical properties of epoxy composites. Even though it is well know that the curing cycle affects the final properties of the composites, up till today the effect of these nanofibrous structures on the curing characteristics of epoxies is not studied in detail. Therefore the influence of nanofibres of different polyamide types (PA 6, PA 6.6, PA 6.9 and PA 4.6) and of polyvinyl alcohol (PVAL) on the curing reaction of a diglycidyl ether of bisphenol A (DGEBA)–methylenedianiline (MDA) system was investigated, using non-isothermal and quasi-isothermal (modulated temperature) differential scanning calorimetry ((MT)DSC) measurements. The effect of the nanofibre fraction and polyamide type is examined, and a comparison with conventional PA 6 fibres is made. For polyamide nanofibres, the accelerating effect seems to result mainly from water present in the nano- and microfibers. PVAL nanofibres accelerated the curing more strongly than the PA nanofibres, though their moisture content was lower, indicating a catalytic effect of the surface hydroxyls.

A “Sandwich” type of neutron shielding composite filled with boron carbide reinforced by carbon fiber

A “Sandwich” type of neutron shielding composite reinforced by carbon fiber was currently studied in view of the rapidly growing need of nuclear protective materials. Comparison to Scanning Electron Microscopy (SEM) analysis of a variety of carbon fiber surface treatment, a new technology, named acetone–resin ultrasonic pretreatment was better to ensure that the carbon fiber and the resin glue were solidified effectively by diffusion as a whole, and also worked out the traditional problem about full impregnation of carbon fiber. Meanwhile, differential scanning calorimetry (DSC) and thermogravimetic analysis (TGA) of the composite filled with boron carbide were observed. The conclusion was that the effect of the acid anhydride type curing agent (B-570) was better than the polyamide type (TY-203) in the field of heat resistance, and the carbon fiber was helpful to improve the thermal stability of the composite when the adding content was 28.2%. In addition, the “Sandwich” type of neutron shielding composite was prepared for the tensile performance test. Compared to the boron carbide particles added directly into the composite, it has a huge performance improvement in the mechanical properties when the content of boron carbide filled with 20%, meanwhile it significantly upgrade the neutron shielding performance with spraying with 0.4mm.

The Water Molecules Dynamic Adsorption Performance Study in the Reverse Osmosis Membrane of Aromatic Polyamide Type

In order to understand the mass transfer process of water molecules in the reverse osmosis membrane based on the dynamic adsorption theory and diffusion transfer concept, according to the theory of random walk, the diffusion-adsorption equation is deduced at the beginning of dynamic adsorption around all diffusion regions. It was studied and analyzed the dynamic adsorption behaviour of H2O in reverse osmosis membrane of polyamide in the experiment, and the influence of the different temperature to the dynamic adsorption of the reverse osmosis membrane on the early stages was discussed, and calculated the abnormal diffusion index dw. The results showed that the water molecules in this aromatic polyamide type reverse osmosis membrane have the behaviour of abnormal dynamic adsorption, and the higher temperature was, the smaller the abnormal diffusion index dw was.

The influence of a polyamide matrix on the halochromic behaviour of the pH-sensitive azo dye Nitrazine Yellow

It is of great interest to introduce pH-sensitive dyes into fibrous materials since this may result in flexible sensor systems. However, to date, the effect of a textile matrix on the halochromic properties of dyes is still unknown which severely limits their further development. Therefore, this paper focuses on an in-depth study of the halochromism of the azo pH-indicator dye Nitrazine Yellow in solution and incorporated in polyamide textile matrices with different structures. Based on both experimental spectroscopic data and computational calculations, an azo hydrazone tautomerism was found to be responsible for the halochromism of Nitrazine Yellow in solution. The hydrazone tautomer was most stable in neutral pH while the deprotonated dye molecule was believed to be an azo tautomer, resulting in a bathochromic shift with increasing pH. This tautomerism was, moreover, also present in the polyamide matrices. However, the equilibrium was clearly affected by the polymeric environment resulting in a shift and broadening of the dynamic pH-range. The polyamide type and textile structure influenced the halochromic response due to different interactions and accessibility of the dye. In conclusion, the halochromism of Nitrazine Yellow is present in all studied systems and is always based on an azo hydrazone tautomerism but the polyamide matrix causes distinct alterations in the tautomeric equilibrium.

Cyclic oligomers in polyamide for food contact material: quantification by HPLC‐CLND and single‐substance calibration

Cyclic oligomers are the major substances migrating from polyamide (PA) food contact materials. However, no commercial standards are available for the quantification of these substances. For the first time the quantification of cyclic oligomers was carried out by HPLC coupled with a chemiluminescence nitrogen detector (CLND) and single‐substance calibration. Cyclic monomer (MW = 226 Da) and dimer (MW = 452 Da) of PA66 were synthesised and equimolar N detection of CLND to synthesised oligomers, caprolactam, 6‐aminohexanoic acid (monomers of PA6) and caffeine (a typical nitrogen calibrant) was proven. Relative response factors (UVD at 210 nm) referring to caprolactam were determined for cyclic PA6 oligomers from dimer to nonamer, using HPLC‐CLND in combination with a UVD. A method for quantification of cyclic oligomer content in PA materials was introduced using HPLC‐CLND analysis and caffeine as a single nitrogen calibrant. The method was applied to the quantification of cyclic PA oligomers in several PA granulates. For two PA6 granulates from different manufacturers markedly different oligomer contents were analysed (19.5 versus 13.4 g kg−1). The elution pattern of cyclic oligomers offers the possibility of identifying the PA type and differentiating between PA copolymers and blends.

Chiral Polyamides Having L-Glutamyl Residue as a Component

Polyamides with chiral environment were obtained from aromatic diamine, 1,3-phenylenediamine (1,3-PDA) or 1,4- phenylenediamine (1,4-PDA), and N-α-benzoyl-L-glutamic acid (Benzoyl-L-Glu). The optical rotation ([α]D) for 1,3- PDA-Benzoyl-L-Glu was determined to be 3.7 deg cm2 g–1, while that for 1,4-PDA-Benzoyl-L-Glu to be 9.7 deg cm2 g–1. 1,3-PDA-Benzoyl-L-Glu showed adsorption selectivity toward D-Glu and its adsorption selectivity was determined to be 1.68. Contrary to this, 1,4-PDA-Benzoyl-L-Glu showed adsorption selectivity toward L-Glu and the adsorption selectivity toward L-Glu was determined to be 1.33. From those results, those two types of chiral polyamide are expected to applicable to chiral separation or chiral recognition.

Diluent filler particle size effect for thermal stability of epoxy type resin

Epoxy resin is used as a material for electrical and electronics molding in various forms but its thermal conductivity must be controlled with various additives on account of its lower conductivity than metal or ceramics. Silicon dioxide (SiO2) and silica were selected as the reinforcement and diluent filler for epoxy resins, respectively. The optimum amount of reinforcement filler, SiO2, was 50wt%. The thermal properties and thermal stability were observed according to silica ratio and particle size. An epoxy modified with a polyamide type hardener showed superior thermal conductivity to that modified with a cyclo-aliphatic amine type hardener. The thermal conductivity increased with increasing silica ratio and particle size. The thermal stability evaluation based on the particle size of silica was in the order of 14/18mesh (1.00–1.16mm)>8/10mesh (1.65–2.36mm)>28/35mesh (0.42–0.59mm). The optimum silica size of the diluent filler was 14/18mesh (1.00–1.16mm). An epoxy type resin transformer with excellent thermal properties and thermal stability could be designed when the mixing weight of epoxy resin was equal to that of the hardener.

Optical resolution of racemic amino acid derivatives with chiral polyamides bearing glutamyl residue as a diacid component

AbstractNovel chiral polyamides with chiral environment in their main chains were obtained from aromatic diamine, 4,4′‐diaminodiphenylmethane (DADPM), and the D‐isomer or the L‐isomer of N‐α‐protected glutamic acid, such as N‐α‐benzyloxycarbonyl‐D‐glutamic acid (Z‐D‐Glu‐OH) or N‐α‐benzyloxycarbonyl‐L‐glutamic acid (Z‐L‐Glu‐OH), in the presence of triphenyl phosphite (TPP). Two types of newly prepared polyamide showed optical rotation, implying that there were asymmetric carbons in their main chains. Circular dichroism studies demonstrated that resulting chiral poly‐ amides took a helical structure. Optical resolution ability of those two types of polyamide was studied by adopting potential difference as a driving force for membrane transport. Membranes showed permselectivity toward racemic mixture of N‐α‐acetyltryptophan (Ac‐Trp). The permselectivity was dependent on the absolute configuration of diacid component. The permselectivity was expressed by diffusivity selectivity, which was determined by the presence of chiral helicity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Thermal deformation of epoxy type resin for neon transformer housing

This study focused on the experimental and theoretical evaluation of the thermal stability of epoxy resins for the development of neon transformer housings. A variety of hardeners was added to the epoxy resin to improve the thermal stability and workability of the neon transformer. Silicon dioxide (SiO 2) also was added as a reinforcement filler. Then, the variation of the viscosity and thermal stability with the amount of reinforcement filler and hardener was evaluated. A hardener modified with cycloaliphatic amine was superior to the polyamide type hardener in terms of the physical properties and the optimum curing conditions were found to be a curing time of 70 min at 343 K. The viscosity of the epoxy resin increased with increasing amount of silicon dioxide (SiO 2), whereas the volume deformation ratio used for the evaluation of the thermal stability decreased. As a result, it was concluded that the polyamide type hardener had superior characteristics in terms of the workability and thermal stability and that the optimum silicon dioxide (SiO 2) content was 50 wt%.

Electrical and thermal properties of polyamide 12 composites with hybrid fillers systems of multiwalled carbon nanotubes and carbon black

Hybrid filler systems of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) were incorporated into two types of polyamide 12 (PA12) using small-scale melt mixing in order to identify potential synergistic effects on the interaction of these two electrical conductive fillers. Although no synergistic effects were observed regarding the electrical percolation threshold, at loadings well above the percolation threshold higher volume conductivities were obtained for samples containing both, MWCNT and CB, as compared to single fillers. This effect was more pronounced when using a higher viscous PA12 matrix. The formation of a co-supporting network can be assumed. The combined use of CB and MWCNTs improved the macrodispersion of MWCNT agglomerates, which can be assigned as a synergistic effect. DSC measurements indicated an effect of the nanofiller on crystallisation temperatures of PA12; however this was independent of the kind or amount of the carbon nanofiller.

Wicking properties of various polyamide nanofibrous structures with an optimized method

AbstractIn comparison with conventional structures, nanofibrous structures have unique characteristics, such as higher surface‐to‐volume ratios, smaller pores, and higher porosity. Their hydrophilic nature is a key characteristic for many applications. However, because of their high porosity, it is difficult to measure the hydrophilicity of nanofibrous structures with contact‐angle measurements. Therefore, characterization through wicking behavior is more appropriate. The International Organization for Standardization norm on wicking needs some refining to account for the specific nature of highly porous nanofibrous structures. A refined method was used on several structures that differed in the fiber diameter and the polyamide type. The structures with the thickest nanofibers had the highest wicking rates. At equilibrium, the wicking heights of structures of different polyamide types with the same average fiber diameter followed the trend expected from their intrinsic hydrophilicity. In the initial phase, the capillary forces established the wicking behavior. Later in the process, the wicking behavior was determined by the capillary forces and the hydrophilicity. In conclusion, the hydrophilicity of nanofibrous structures can be successfully determined by an optimized wicking procedure, and the fiber diameter is the dominant parameter for the resulting wicking height at equilibrium. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Aging behavior of polymeric solar absorber materials – Part 1: Engineering plastics

In this series of two papers, various polymeric materials are investigated as to their potential applicability as absorber materials for solar thermal collectors. The focus of the investigation is to study the aging behavior of these materials under maximum operating conditions (80 °C in water up to 16,000 h) and stagnation conditions (140 °C in air up to 500 h) typical for northern climate. The materials supplied or produced as polymer films were first characterized in the unaged state and then for different states of aging by differential scanning calorimetry (DSC), by size exclusion chromatography (SEC) and by mechanical tensile tests. Physical aging phenomena were studied by DSC, SEC analysis provided information on chemical degradation of the materials. In addition, physical and chemical aging were both analyzed via the small and large strain mechanical behavior. While the present Part 1 of this paper series deals with the aging behavior of engineering plastics, including two amorphous polymers (a polyphenylene ether polystyrene blend (PPE + PS) and polycarbonate (PC)) and two semi-crystalline polymers (two types of polyamide 12 (PA12)), the aging behavior of so-called “commodity” plastics (PE and PP) is the subject of Part 2. Comparing the two aging conditions, the amorphous materials (PPE + PS and PC) turned out to be more prone to physical and chemical aging at 140 °C in air. In contrast, the semi-crystalline PA12 materials were more strongly affected by exposure to water at 80 °C, although to different degrees, depending on the modification.

Localization of carbon nanotubes at the interface in blends of polyamide and ethylene–acrylate copolymer

The present study demonstrates for the first time the possibility to jam unpurified and unfunctionalized multiwall carbon nanotubes (MWNTs) at the interface of an immiscible blend of polyamide (PA) and ethylene–acrylate (EA) copolymer. The confinement appears to be stable. The influence of the mixing strategy and of the polyamide type used has been examined. When the MWNTs are first dispersed in PA6, most of them migrate to the interface although some of them stay in the PA phase. When the MWNTs are first dispersed in PA12, they remain well dispersed in PA. When the MWNTs are first dispersed in the EA copolymer or when the three components are simultaneously mixed, a large part of the MWNTs migrate to the interface whatever the PA used. However, some of the MWNTs remain in the EA phase and when PA12 is used, part of the MWNTs penetrate inside the PA nodules. By a combination of TGA and separation techniques, we show that the first polymer to come in contact with the nanotubes during melt mixing is (at least partially) adsorbed irreversibly, by non-covalent adsorption. The resulting modification of interfacial thermodynamics explains the observed confinement.

Influence of the structures of polyamide 6 fibers on their ageing under intensive insolation conditions

The effects of large doses of UV radiation, relating to actual operational use during 1, 2 or 5 summer seasons, on changes of chemical structures, crystalline structures, morphology and tensile properties of four types of polyamide 6 were investigated. The fibers differed in cross-section shape and mat degree caused by TiO2 addition. The fibers were tested using, among others, SEM and IR methods. Critical dissolution time (CDT) was also investigated.

Indigo Dyeing of Polyamide Using Enzymes for Dye Reduction

Classical processes of indigo dyeing use sodium dithionite as reducing agent, causing enormous environmental problems. In this paper, a new process of indigo reduction using NADHdependent reductases from Bacillus subtilis in the presence of redox mediators is presented. The efficiency of mediated enzymatic indigo reduction on the dyeing of decitex polyamides 6 and 6,6 was studied at 60 °C, pH 7 and 11, and different indigo concentrations. The color values and color fastness properties (to wash, light and perspiration) were evaluated and compared to chemically indigo-dyed polyamides. The results indicated that the dyeing properties were pH, time and polyamide type dependent, resulting in the greater color depth of morphologically more amorphous polyamide 6,6 dyed at pH 11 for 90 minutes. Both the alkaline and acid perspiration fastness properties of the dyeings were very good, whereas the dyeings displayed poorer fastness of 3—4 to light and wash. Successful reuse of the enzyme was confirmed.

Effect of Intermolecular Interactions and Cooling Rates on Crystallization Behaviors of Polyamide 6 Blends

Three types of polyamide 6 based blends are prepared, in which the intermolecular interactions are different, ranging from ‘no interaction’ to strong interaction. Under two extreme cooling conditions, the melts of the blends crystallized and then the crystalline structure and melting behaviors are examined, respectively. The results suggest that depending upon the degree of intermolecular interaction and the amount of the second component, PA6 may have different crystal forms.

Codend selection in the deep-water crustacean trawl fishery in Portuguese southern waters

In this paper, the potential improvement of size-selectivity by increasing codend mesh size and changing twine type is addressed for the main commercial species exploited by crustacean trawlers in waters off the Portuguese south coast. Three cruises were conducted between autumn 1998 and summer 1999 onboard the F/V “Porto Bravo”, resulting in a total of 93 valid hauls using 3 different sizes of diamond mesh in the codend (stretched nominal sizes of 55, 70 and 80 mm) and 2 types of twine, polyamide and polyethylene. A non-linear mixed-effects model was employed to include the effect of covariates and between-haul variation in the estimation of codend selectivity parameters for the main target species in this fishery, Norway lobster, Nephrops norvegicus (L.), rose shrimp, Parapenaeus longirostris (Lucas 1846), and ‘blue and red’ shrimp, Aristeus antennatus (Risso, 1816). The chosen selectivity model found a significant ( p < 0.001) linear effect of mesh size for all three target species, and a significant effect of cruise for Norway lobster ( p < 0.05) and rose shrimp ( p < 0.001). The cruise effect was due to a difference between the autumn 1998 cruise and the two latter cruises. This effect coincides with a change from polyamide twine in the autumn cruise to the use of polyethylene twine in the latter cruises. Other covariates, such as depth, codend-catch weight and species catch weight did not show any systematic effect on selectivity and thus were not included in the final models. The retention of a high number of undersized (or immature) individuals, while using the legal minimum mesh sizes, suggests the need for a change in the status quo fishing pattern.

Comparison of nanocomposites based on nylon 6 and nylon 66

Nylon 6 and nylon 6,6 organoclay nanocomposites were prepared by melt processing using a twin screw extruder. The effects of polyamide type and processing temperature on the mechanical properties and the morphology of the nanocomposites were examined. Mechanical properties, transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), percentage crystallinity and isothermal thermo-gravimetric analysis (TGA) data are reported. A particle analysis was performed to quantitatively characterize the morphology; these results are later employed in modeling the modulus of these materials using composite theory. No significant difference was observed in the mechanical properties and morphology of PA-6 nanocomposites processed at two different temperatures. PA-6 nanocomposites had superior mechanical properties than those made from PA-66. The tensile strength of PA-66 nanocomposites deviated from linearity at high levels of MMT. WAXD and TEM results show that the PA-6 nanocomposites are better exfoliated than the PA-66 nanocomposites, which exhibit a mixture of intercalated and exfoliated structures. Mechanical properties were consistent with the morphology. DSC reveals a higher percentage of crystallinity in the PA-66 samples. Isothermal TGA shows only a 5% difference in the degradation of the organic modifier on the organoclay processed at 240°C versus 270°C. Particle analysis shows a higher average particle length and thickness, and a lower average particle density and aspect ratio in nanocomposites based on PA-66 versus PA-6. The Halpin-Tsai and Mori-Tanaka composite theories predict satisfactorily the behavior of the PA-6 nanocomposites, while the PA-66 nanocomposites were predicted acceptably up to a certain volume fraction where the non-linear behavior takes effect. All the results indicate that there is a lower degree of exfoliation in the nanocomposites produced with a PA-66 matrix apparently stemming from the chemical differences between PA-6 and PA-66.